December 27, 2013

Your Eating Affects Your Brain

From time to time, studies show the difference in brain development between conservative and progressive thinkers. Recently, however, a new reason for diversity in brain configuration has a novel approach—gut bacteria.

“I’m always by profession a skeptic,” says Dr. Emeran Mayer, a professor of medicine and psychiatry at the University of California, Los Angeles. “But I do believe that our gut microbes affect what goes on in our brains.” He hypothesizes that brain structure is molded by bacteria in digestive systems as people mature, influencing adult moods, behavior, and feelings. To check out his theories, Mayer is using MRI scans on thousands of volunteers and then comparing the brain structure to the bacteria types in their intestines.

Mayer also studied the effects of probiotics on the brain. He and his colleague Kirsten Tillisch gave healthy women yogurt containing a probiotic and then scanned their brains. Subtle signs indicated that the brain circuits involved in anxiety were less reactive, according to a paper published in the journal Gastroenterology.

In examining gut microbes in mice, other researchers have seen changes in both brain chemistry and behavior. One experiment involved replacing the gut bacteria of anxious mice with bacteria from fearless mice. “The mice became less anxious, more gregarious,” says Stephen Collins of McMaster University in Hamilton, Ontario, who led a team that conducted the research. Reversing the process, bold mice became timid. Also aggressive mice calmed down when scientists changed their microbes by changing diet, feeding them probiotics, or giving them antibiotics.

Researchers in Baltimore are testing a probiotic to see if it can help prevent relapses of mania among patients suffering from bipolar disorder. “The idea is that these probiotic treatments may alter what we call the microbiome and then may contribute to an improvement of psychiatric symptoms,” said Faith Dickerson, director of psychology at the Sheppard Pratt Health System.

“It makes perfect sense to me,” says Leah, a study participant who has been diagnosed with bipolar disorder and asked that her full name not be published. “Your brain is just another organ. It’s definitely affected by what goes on in the rest of your body.”

Mayer has also been studying the effects of probiotics on the brain in humans. Along with his colleague Kirsten Tillisch, Mayer gave healthy women yogurt containing a probiotic and then scanned their brains. He found subtle signs that the brain circuits involved in anxiety were less reactive, according to a paper published in the journal Gastroenterology. The study was funded by Danone, a company that produces yogurt and other dairy products.

Collins and his colleagues also found changes in a part of the mice’s brains involved in emotion and mood, including increases in a chemical called brain-derived neurotrophic factor, which plays a role in learning and memory.

One reason for the connection between abdomen and brain may be the vagus nerve which between the two parts of the body. After researchers in Ireland cut the vagus nerve in mice, the brain did not appear to respond to any bacterial changes in the gut. “The vagus nerve is the highway of communication between what’s going on in the gut and what’s going on in the brain,” says John Cryan of the University College Cork in Ireland, who has collaborated with Collins.

Altering gut microbes could also correct problems such as autism. Many autistic behaviors in mice disappeared or were strongly ameliorated with probiotics, said Paul Patterson at the California Institute of Technology in Pasadena (CA).

Gut microbes may also modulate the immune system or produce their own versions of neurotransmitters. “I’m actually seeing new neurochemicals that have not been described before being produced by certain bacteria,” says Mark Lyte of the Texas Tech University Health Sciences Center in Abilene, who studies how microbes affect the endocrine system. “These bacteria are, in effect, mind-altering microorganisms.”

Researchers have known that the brain sends signals to the gut, which is why stress and other emotions can contribute to gastrointestinal symptoms. This study shows what has been suspected but until now had been proved only in animal studies: that signals travel the opposite way as well.

Gut bacteria may also cause obesity, as shown by studies with mice. Researchers are considering the idea that changing bacteria in a person’s intestine could cause weight loss in overweight people, basing their hypothesis on studies of identical twin mice. Mice that ate food high in fat and low in fruits and vegetables kept the gut bacteria that caused weight gain.

Studies have shown that conservatives suffer far more from fear and anxiety. If they changed their intestinal bacteria, would they change their politics?